Various luminescent devices have hitherto been proposed which employ an organic electroluminescent (EL) element comprising electrodes and interposed therebetween a luminescent layer comprising an organic EL material. As compared with inorganic EL elements, the organic EL elements themselves luminesce upon application of a lower voltage, have a higher degree of freedom of material design, and can be more easily made thin. The organic EL elements are hence expected to be used as surface light sources for use as, for example, the backlights of liquid-crystal displays.
However, the conventional organic EL devices have had a problem that the efficiency of light utilization is low. Specifically, the efficiency of emission η of light generated by a luminescent layer (efficiency of taking out the light) is approximated using the equation η=½n2, wherein n is the refractive index of the luminescent layer. Supposing that n is 1.6, the value of η is about 0.2, i.e., the efficiency of emission is as low as about 20%. It has been proposed to heighten the efficiency of emission by a technique in which the light generated in an element is transmitted by total internal reflection and emitted through an edge of the element, by a technique in which a luminescent layer comprising a discotheque liquid crystal is formed to enhance light emission toward the front side, or by a technique in which a light diffuser film is disposed outside an element to reduce total internal reflection (see JP-A-6-160842 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”), JP-A-10-321371, and JP-A-8-83688). However, these techniques have drawbacks of complicated constitution, device instability, insufficient efficiency of emission, etc., and none of them is a satisfactory measure for resolution.